From the November 2017 issue

Has a meteorite ever been found that is suspected to have come from a solar system other than our own? How would we recognize such a meteorite?

Michael Rodriguez Corvallis, Oregon
By | Published: October 3, 2017
NWA 869 is an ordinary chondrite, the most common type of stony meteorite found on Earth. Planetary geologists believe these objects originate from asteroids.
James St. John
Most (99 percent) of the meteorite inventory on Earth comes from the main asteroid belt, between the orbits of Mars and Jupiter. A small fraction of meteorites come from Mars (about 180) and the Moon (about 275). Some meteorites have been suspected to come from comets. Famous astronomer Carl Sagan once said, “It is unlikely that a single meteorite of extrasolar origin has ever reached the surface of the Earth.” Numerical calculations suggest that the possibility of exchange of meteoritic fragments between stellar systems is highly unlikely. Indeed, extrasolar meteorites have not been identified in our meteorite collections.

Although we don’t have extrasolar meteorites, “presolar” materials have been found in some primitive meteorites. These materials are called presolar because they were created in stars before our solar system formed and were transported to our protosolar nebula. We can identify these tiny grains, which range in size from a nanometer to a few micrometers, based on their anomalous isotopic compositions. There is also evidence for the delivery of material from nearby supernovae at least twice within about the last 10 million years. This material was deposited on Earth and is identified based on the isotopic anomalies found in ocean sediments. However, we don’t have actual rock fragments from outside our solar system.

If extrasolar meteorites do exist, their chemical, mineralogical, and isotopic composition would be important signatures of their origin. But how different or similar these signatures would be, compared to our own solar system material, is left to speculation for now.

Prajkta Mane  
Postdoctoral Research Associate, Department of Planetary Sciences and Lunar and Planetary Laboratory,   University of Arizona, Tucson, Arizona